Abstract New Chemical Tools for Visualizing Cellular Physiology The cell membrane is the only organelle shared by all varieties of cellular life. Unequal distribution of ions and chemical species across the plasma membrane results in the generation of an electrochemical potential, and rapid changes in this membrane potential, or voltage, drive the unique physiology of excitable cells like neurons and cardiomyocytes. However, all cells, even non-excitable cells, possess a membrane potential, and mounting evidence supports a role for membrane potential in controlling fundamental cellular physiology?for example, cell cycle, migration, proliferation, and differentiation?in non-excitable cells. Despite the central role of membrane potential to the cellular physiology of both excitable and non-excitable cells, our understanding of membrane potential in these systems remains incomplete, due in large part to a lack of tools for studying cellular physiology with high spatial and temporal resolution. Measurements of membrane potential rely on highly invasive, low throughput direct voltage recording through electrodes (patch clamping) or by indirectly monitoring the down-stream effects of membrane potential via imaging (Ca2+ imaging). We propose to use the power of synthetic organic chemistry to design fluorescent voltage sensors to probe membrane potential dynamics in neurons and cardiomyocytes, in addition to non-excitable cells. In a complementary approach, we are developing small molecule-based activity integrators that integrate Ca2+ transients over time to enable high resolution reconstruction of cellular activity during a specified time window?at length scales (superresolution microscopy, electron microscopy) that are not accessible with currently available sensors. Although many of the tools we are developing have applications in neuroscience, these strategies and techniques can be applied to fundamental cellular physiology. Additionally, my research program places a heavy emphasis on synthetic chemistry and molecular design to achieve our goals. I anticipate we will uncover fundamental insights in areas related to photoinduced electron transfer, supramolecular chemistry, physical organic chemistry, and biophysics as we design and develop these new tools.